Camshaft adjusters are industrial modules for adjusting the phase angle between a crankshaft and a camshaft in an internal combustion engine. One of the components, also known as the stator, is rotatably fixedly connected to the crankshaft. The other component, also known as the rotor, is rotatably fixedly connected to the camshaft and rotatably supported relative to the stator. In a hydraulic camshaft adjuster, the stator usually includes a number of separating elements, between which a vane element of the rotor is situated. The vane element divides the space between two adjacent separating elements into an advance chamber and a retard chamber. Both chambers are connected to switchable pressure medium lines. If a pressure medium is applied to the advance chamber via the associated pressure medium line, and if the pressure medium line of the retard chamber is connected to a pressure medium outlet, the rotor is moved in an advance direction with respect to the stator and vice versa. If pressure medium is applied to both chambers, or if the pressure medium lines are blocked, the rotor is hydraulically fixed at the set phase angle with respect to the stator.
The hydraulic camshaft adjuster is usually integrated into the lubricant circuit of the internal combustion engine for the purpose of supplying pressure medium. In a start phase of the internal combustion engine, the pressure of the lubricant (oil pressure) is generally not yet sufficient for flawless operation of the camshaft adjuster. The rotor may oscillate in an uncontrolled manner within the permitted angular range and possibly strike the stator, which results in an undesirable acoustic abnormality. For this reason, hydraulic camshaft adjusters usually have a mechanical locking device which locks the two components which are rotatable relative to each other, i.e., the rotor and stator, in a defined angular position with respect to each other during a standstill or in a start phase of the internal combustion engine. Due to the building pressure of the lubricant, the lock is released, so that the rotor and stator may be adjusted with respect to each other during operation of the internal combustion engine.
The angular position in which the rotor and stator of a hydraulic camshaft adjuster are mechanically locked with respect to each other is usually indicated as an advance or a retard. In other words, in the locked angular position, the rotor strikes a separating element in either in the advance position, i.e., for example in the clockwise direction, or in the retard position, i.e., for example in the counterclockwise direction. A hydraulic camshaft adjuster is also known from EP 0 799 977 A1, in which the two rotatable components are locked to each other in a central angular position between the advance position and the retard position during the standstill. This provides thermodynamic advantages for the correspondingly operated internal combustion engine. In this position, a locking bolt on the one component engages with a correspondingly situated central slotted gate on the other component for the purpose of locking.
A camshaft adjuster of the type mentioned at the outset is known from EP 1 672 187 A1. A central slotted gate is provided herein, with which both locking bolts engage in a central angular position when the two components are locked with respect to each other. Due to this design, a simplified locking of the components in the central position is possible. When the rotating components are locked, one of the locking bolts first enters the central slotted gate, which is widened accordingly in the direction of rotation, and forms a stop therein only upon further rotation. In the defined stop position, the second locking bolt may enter the central slotted gate, so that the two components finally lock in both directions of rotation in a fixed angular position with respect to each other.
A camshaft adjuster of the type mentioned at the outset is also known from DE 10 2005 060 829 A1. Two locking bolts for locking the two components in a central angular position are provided herein, each of which engages with a separate central slotted gate. A third and a fourth locking bolt are additionally provided, which lock the components in an advance position and in a retard position with respect to each other via a first and a second end slotted gate.
Finally, a camshaft of the type mentioned at the outset is also proposed in DE 10 2007 007 073 A1. Herein, the components of the camshaft adjuster may be locked in a total of three different positions with respect to each other, namely in an advance position, in a retard position and in a central adjusting position, with the aid of a total of three locking bolts and three slotted gates.